Shower pipes

Hi all. Maybe yet another stupid question.
I have had trouble recently installing a thermostatic shower onto new pipes. They had to be cut so tight to the tiles that it was awkward to get the nut and olive to bite and seal. Is it always as tight and what is the normal length of pipe you need? The instructions were as helpful as a chocolate fire guard and stated enough pipe. I couldn't get my pipe slice close enough for what was needed. Any ideas on how to make it easier / do it better next time?

You need a lot more of a description then you have provided. Post a picture.

I think this is what he might be talking about.

I put a similar one in a couple months ago like this one.
The one I took out used 5/8" copper stub outs with compression nuts and ferrules. Just like installing a compression angle stop.
The one I installed used threaded nipples like and old wall mount so I had to open the back wall to make some changes.

installation guide
Quoted from Guide ^^

INSTALLATION
The valve must be installed with the HOT water coming in on the left and
the COLD on the right, when the outlet is positioned on top. The inlet elbows
are fitted with 15mm olives and compression nuts. It is important that all the
pipe work should be thoroughly flushed through before connecting the
valve.

they make a 1/2" brass sweat adapter

that is just like the 1" sweat adapter in a flush valve sweat kit

little buggers are perfect for when someone forgets to stub out a nipple, and stubs out copper